This invention is directed to a thread connection in general, and in particular to the thread of a filter cartridge, and to the filter cartridge comprising such a thread. More particularly, the thread has a reversed load flank, which allows to prevent ripping out of the cartridge from its base.
Vehicles equipped with a combustion engine, comprise several filters that have to be changed during the maintenance operations. Theses filters are usually disposable cartridges, which are directly fixed to the engine through a base, or placed in a bowl or a housing, which is fixed to the engine. In most cases, the cartridge or the bowl is threaded in such a way that it can be screwed on the base. Threaded connections are usually formed using metric ISO standard thread. Some specific shape may also be used like in U.S. Pat. No. 7,997,842. Those conventional thread connections allow the manual tightening of the cartridge or the bowl containing the filter. However, those threads are not adapted for resisting high ripping out forces, In case of prolonged internal pressure, or overpressure, or in case the cartridge is not properly tightened, then the cartridge can be ripped out. Therefore, it is desirable to prevent accidental rip out of the cartridge while maintaining the easiness of the manual tightening. This is particularly true for an air-dryer filter cartridge for compressed air systems of a truck.
It is therefore desirable to secure the cartridge or the bowl containing the cartridge on the base.
An air-drier cartridge of brake system of a truck is particularly exposed to high puts ting pressures. The pulsating pressure is transmitted to the threads. These repeated constraints can induce tiredness of the thread connection, and thus initiate a dissociation of the air-drier cartridge from its base. This can limit the time of use of a cartridge or the bowl containing the cartridge.
It is therefore desirable to allow a prolonged usage of the cartridge or the bowl containing it, by limiting the effects of the tiredness on the threads. The present thread connection improves the life time of a disposable filter cartridge. This allows to limit the maintenance operations.
The thread of the present invention is made in such a way to increase the cohesion of the assembly in case a ripping out force is applied. In particular, the thread of the present invention increases the cohesion force of the assembly only during the application of a ripping out force. The thread of the present invention is designed to increase the cohesion force of the assembly as long as the ripping out force is increasing. In other words, the cohesion force is increased proportionally to the increase of the ripping out force. The ripping out force may be a pressure internal to the cartridge or the bowl containing the cartridge. However, any external force which tends to dissociate the threaded parts of the assembly is considered as a ripping out force.
The threaded assembly according to the present invention comprises a first and a second part, also considered as a male part, and a female part, which is complementary to the male part. The female part of the assembly may correspond to the threaded part of the cartridge or the bowl containing the cartridge. The male part of the assembly may correspond to the threaded part of the base on which the cartridge is screwed. However, the opposite configuration, wherein the male part of the thread assembly is located on the cartridge or the bowl comprising the cartridge, and the female part of the thread assembly is located on the base, is also possible. In any of these configurations, the load flank of the threads has a reversed angle. This means that the threaded part of the cartridge is oriented rearward to the screwing axis of the cartridge. In case of a bowl, the threaded part of the bowl is oriented rearward to the screwing axis of the bowl. The screwing axis is to be understood as the axial direction to which the cartridge or the bowl containing the cartridge is screwed on the base, from an open position to a fully tightened position against the base. The load flank of the thread is the flank that takes the applied axial load in the threaded assembly. In case of an air-drier cartridge, the load flank is the part of the thread on which the internal air pressure is applied. Due to the reverse inclination of the threaded part of the cartridge, the air pressure applied to the cartridge improves the interaction between the base and the cartridge. In other words, the surface of contact between the male part and the female part of the threaded assembly tends to increase when an internal pressure is applied, thus allowing a stronger tightening of the cartridge onto the base. The surface of contact corresponds to the surface of the load flank of the first part of the threaded connection, which is in direct contact with the corresponding load flank of the second part of the threaded connection. In addition, the surface of contact may include the surface of the crest of the first part of the threaded connection which is in direct contact with the root of the second part of the threaded connection. The surface of contact increases when the clearance between the two parts of the threaded connection decreases, and in particular the clearance between the crest of the first part of the threaded connection and the root of the second part of the threaded connection.
Due to the reverse angle of the load flank, an increase of the internal pressure or any other ripping out force applied to the cartridge, tends to bring closer the crest of the first part and the root of the second part of the threaded connection. Under such conditions the clearance between the two parts of the threaded connection is minimized.
In practice, the thread of the present invention allows to bring closer the two parts of the threaded connections when a ripping out force is applied to the cartridge.
Therefore, the present invention is directed to a threaded assembly wherein the load flank has a reversed angle. The preferred assembly is an assembly of an air-drier filter cartridge, or a bowl containing an air-drier filter cartridge, and the base on which it is screwed. However, any threaded assembly which needs to resist against ripping out constraints are also encompassed. The present invention is further directed to a cartridge comprising a threaded portion, whereby the load flank is inclined rearward to the screwing axis of the cartridge. The cartridge is preferably a disposable cartridge, and more preferably an air-drier filter cartridge.
The invention also encompasses a vehicle equipped with the cartridge above mentioned, and the assembly of said cartridge with the corresponding base. The vehicle is preferably a medium or heavy duty vehicle like a truck, a bus, or any other industrial vehicle.